1. Field of the Invention
The present invention is directed to load-bearing structural members of a prestressed plastic foam material.
2. Description of Related Art
Heretofore, polymer foam materials, have been used in the building construction industry, primarily as insulation materials. The low density and low weight of plastic foam combine to make it a desirable insulation material, whether in panel form (expanded) or loose bead form (expandable).
Foam panels have been used, for example, to provide an insulative layer between walls separated by studwork or other framework. Loose plastic foam can be "blown" into voids, cavities, or other empty spaces to fill or partially fill such cavities, thereby improving the insulative characteristics of the structure. Plastic foams also possess good resistance to water vapor transmission in these and other applications.
Plastic foams are also known to possess relatively good structural strength, provided the material is fairly thick, although they have been primarily employed in load bearing applications only in combination with more widely recognized structural materials. An example of this is a use in a sandwich panel where the plastic is employed as an insulative core material. The light weight of foam panels, however, would make it a very desirable material of construction provided sufficient strength could be achieved in thicknesses comparable to other standard construction materials for which it could be used as a substitute.
Useful foam plastics are polyethylene foams, polypropylene foams, structural ABS foams, rigid polyurethane foams, polystyrene foams and phenolic foams. Of these polyurethane foams are preferred.
Prestressing, through various techniques, has previously been used in connection with concrete structural members as an approach to improving the relatively poor tensile strength of concrete. Concrete building materials, while exhibiting high strengths, are also quite heavy and cumbersome to build with, usually requiring heavy equipment for movement and placement of elements. In certain construction applictions, particularly residential home building, use of such heavy members and heavy equipment is undesirable, and in some instances not feasible.
It is therefore a primary object of the present invention to provide a lightweight plastic foam structural member having improved physical properties for use in load-bearing applications.
It is a further object of the present invention to provide a prestressed plastic foam structural member for use in various building and construction applications.
It is a further object of the present invention to provide a plastic foam structural member having one or more prestressed flexible lines or cords traversing the interior of the member to improve the strength characteristics of the structural member.
It is a further object of the present invention to provide a prestressed plastic foam structural member having one or more protective skin layers.
It is yet a further object of the present invention to provide a method for fabricating a lightweight plastic foam structural member having improved strength characteristics.